Solutions that work :
1) Disable "PEG Force X1".
2) Set the NB Vcore to 1.45 v or below.
3) Overclock or underclock the PCI Express reference clock (up to 15 MHz either way). More details here - PCI-E Reference Clock.
4) Set PCI Synchronization Mode to Auto. This is an important step.
5) Set PEG Link Mode to Normal (instead of Auto).